The present invention relates to a display panel having an organic layer which emits light in response to impression of electricity, and also relates to its manufacturing method.
Liquid crystal display panels have been used as a color image display device in various fields instead of a cathode ray tube. Such an image gained by the liquid crystal panel is hardly distinguished in accordance with a visual angle or lightness of the circumference, since the image is reproduced by light which passes through a liquid crystal layer from a back light source.
On the other hand, an electroluminescent (EL) display panel reproduces an image by planar emission, so that the image is distinguished with sufficient resolution even in a dark place without affection of a visible angle.
Various inorganic and organic compounds have been proposed so far for EL material. Especially, organic compounds are expected as an EL layer which can reproduces a bright image with saved power consumption. A display panel involving an organic EL layer has the structure as shown in FIG. 1, wherein striped transparent electrodes (anode) 2, a hole-transporting layer 3, an organic luminous layer 4 and striped backside electrodes (cathode) 5, which extends along a direction crossing the transparent electrodes with a right angle so as to make up X-Y matrix, are successively laminated on a transparent substrate 1. A protective layer 6 is further formed on the backside electrodes 5.
When a drive current is supplied to a predetermined position on X-Y matrix, a hole from the anode 2 recombines with an electron from the cathode 5 in the organic luminous layer 4. An organic luminous molecule in the layer 4 emits light due to excitation by the recombination. The resultant planar emission is observed through the transparent electrodes 2 and the transparent substrate 1.
Leakage of an electric current is intercepted by an insulating layer 7 with a grate pattern interposed between the transparent electrodes 2 and the backside electrodes 5, so as to inhibit unfavorable light emission (so-called xe2x80x9ccross-talkxe2x80x9d) at a part other than the predetermined position of X-Y matrix or at a part near the predetermined position, as shown in FIG. 2. For instance, Jap. Pat. No. 2911552 discloses formation of an insulating layer 7, which opens at a crossing point of the transparent electrodes 2 with the backside electrodes 5 but has an opening space smaller than the crossing area.
Since an organic EL substance is easily decomposed or denatured by humidity or a solvent, an insulating layer 7 is made of material which is free from water or a solvent or scarcely contains water or a solvent. In this regard, a stable polymer such as polyimide or an inorganic substance such as metal oxide is necessarily used without free choice of material for the insulating layer. However, use of an expensive polymer such as polyimide causes price increase of an organic EL display device. Formation of an insulating layer 7 from an inorganic substance requires a dry etching step for patterning, so that a manufacturing process is complicated and resulted in increase of a manufacturing cost.
The present invention aims at provision of a new organic EL display panel with high resolution at a low cost. An object of the present invention is to form an insulating layer from a cheap photoresist without complication of a manufacturing process.
The organic EL display panel proposed by the present invention comprises transparent electrodes, an insulating layer shaped to a grate pattern, an organic luminous layer deposited on the transparent electrodes through apertures of by the insulating layer and backside electrodes successively laid on a transparent substrate. The insulating layer is made of a baked photoresist.
The organic luminous layer may be a monolayer or multilayer including an organic luminous substance, or a bilayer of a hole-transporting layer 3 and an organic luminous layer 4, as shown in FIGS. 1 and 2.
A photoresist for an insulating layer is selected from positive novolac, negative cyclized rubber and chemical amplified photoresists. Black pigment or dye may be added to the photoresist. A cathode separator may be laid on the insulating layer made of the photoresist.
The new organic EL display panel is manufactured as follows: A positive novolac, negative cyclized rubber or chemical amplified photoresist is applied onto a transparent substrate, on which transparent electrodes are pre-formed in a striped shape. The applied photoresist is shaped to a grate pattern and then baked to remove a solvent and moisture therefrom. Thereafter, an organic luminous monolayer or multilayer containing an organic luminous substance and backside electrodes are successively laid on the insulating layer. In case of formation of a cathode separator, the cathode separator is laid on the insulating layer which has been converted from the photoresist by pre-baking.